Archibald Thorburn is high in key: pale, luminous, and filled with optical air. Archibald Thorburn builds on cool foundations: the palette favours the blue-cyan-green arc. The absence of saturated colour is itself an expressive choice: this is a palette of restraint and atmosphere. Only 7.7% is devoted to #917650, yet that small allocation delivers the palette's entire chromatic tension. The palette spans 52 value units: a measured range that delivers coherence over drama. The mid-to-high key, cool bias, and moderate chroma point to outdoor observation - sky and diffused daylight as the dominant light source. This is palette 1 of Archibald Thorburn's sequence - a single chapter in a chromatic story told across many works.